Glucose Assay

Question 1

What are possible sample types for glucose assays?

Answer 1

• food
• Blood
• Urine
• CSF

Question 2

Why should food be used to estimate glucose?

Answer 2

In food analysis to determine the glucose composition of foods, e.g. health risks

Question 3

Why would we estimate glucose in blood?

Answer 3

Used as a marker in blood to diagnose patients with diabetes

Question 4

Why would we examine glucose estimation of urine?

Answer 4

Also used as a marker in urine to diagnose patients with diabetes

Question 5

Why would we estimate glucose in CSF?

Answer 5

Analysis of the CSF provides invaluable insight into pathogenic derangements of the nervous system.

Lowered CSF glucose (hypoglycorrhachia) is seen in meningitis

Question 6

What are the 2 general methods of glucose assays?

Answer 6

Non-enzymatic assays and Enzymatics

Question 7

Differentiate enzymatic and non-enzymatic methods of glucose assays?

Answer 7

The non-enzymatic assay indicates the presence of all reducing sugars, whereas the enzymatic assay is specific for glucose.

Question 8

What substances may interfere with non-enzymatic assays?

Answer 8

Glutathione and vitamin C are 2 reducing substances that can interfere with non-enzymatic assays

Question 9

Give examples of Non-enzymatic assays

Answer 9

• Benedict’s test
• Fehling’s test
• Barfoed’s test
• Dinitrosalicyclic acid

Question 10

Give examples of enzymatic assays

Answer 10

• Hexokinase method
• Glucose dehydrogenase method
• Glucose oxidase/peroxidase

Question 11

What is the reaction scheme of the Hexokinase glucose assay?

Answer 11

• Glucose+ ATP+ HK —> ADP + G6P

- G6P + NAD +G6PDH —> 6 P-gluconolactone + NADH + H

Question 12

What is the reaction scheme of oh glucose dehydrogenase (DH)?

Answer 12

Glucose+ NAD+ GDH —> gluconolactone + NADH + H

Question 13

What is the reaction scheme of glucose oxidase/peroxidase( GOD/POD)?

Answer 13

• Glucose + O2 + H2O + GOD —> Gluconic acid + H2O2

- H2O2 + POD —> H2O + oxidized chromogen

Question 14

What are the characteristics of Enzymatic assays?

Answer 14

• specific for glucose.
• more time consuming
• More costly
• Requires more diligence in handling

Question 15

What is the theory behind the Glucose oxidase/ peroxidase method for glucose estimation?

Answer 15

B-D-glucose + H2O + O2 —> (glucose oxidase) —> D-gluconic acid + H2O2

Peroxide converts DH(colorless) POD to oxidized chromogen/ D (brown)

The intensity of colour produced (measured spectrophotometerically at 450 nm) is proportional to the amount of glucose